Abstract: An optical clock comprises a laser oscillator and modulating means arranged to cooperate with the laser oscillator to produce a series a series of phase-modulated optical pulses. The optical clock further comprises an optical fibre arranged to provide compression of the optical pulses, and may also comprise a step-recovery diode arranged to pulse-pick pulses output from the fibre to produce a series of optical clock pulses, depending on the mode of operation of the modulating means. Phase-modulation is carried out a frequency which provides sufficient linewidth broadening to inhibit stimulated Brillouin scattering within the optical fibre. An optical clock of the invention provides a robust and reliable alternative to clocks based on modelocked lasers, and may be assembled from inexpensive, commonly-available components. The repetition rate of a clock of the invention may easily be adjusted by electronic means. Unlike many modelocked lasers, a clock of the invention does not require precise optical alignment.

Abstract: This invention relates to a method for determining the reply efficiency of a DME navigation beacon and to an apparatus for performing the method. The invention involves locating an RF receiver nearby a DME beacon to be tested. The RF receiver analyses all signals received on the interrogation frequency of that beacon to determine pulse pairs which correspond to a valid interrogation of that beacon. Other pulse events of interest may also be detected. The RF receiver also records all signals on the reply frequency of the beacon and detects all replies sent by the beacon. Particular interrogations can then be correlated with replies and the reply efficiency of the beacon determined. Several RF receivers may be located round the beacon to better provide correlation between particular interrogations and responses.

Abstract: A method of target recognition performs a 3D comparison of target and reference data. Translation invariant signatures are derived from the two data sets, and an estimate of the orientation of the target with respect to the reference is obtained. Rotational alignment and comparison can then be achieved. The 3D data sets can be represented on an axi-symmetric surface such as a sphere and rotational convolution, over a discrete set of selected rotation angles can be performed. Optic flow can be used to derive the estimate of orientation or the target relative to the reference, in terms of a displacement field.

Abstract: A communications system incorporates a transmitter a receiver. The transmitter includes an infrared light emitting diode (LED). The LED output is positive or negative luminescence, i.e. above or below an equilibrium background intensity level respectively, according to the polarity of its bias signal. The receiver contains a lens to focus light from the LED onto a diode detector, from which signals pass to an amplifier, decoder and printer. Output signals from the LED have an average intensity equal to the equilibrium background intensity level and a frequency greater than 100 Hz or byte rate greater than 100 bytes/sec. They are not discernible by conventional thermal infrared imagers with frame rates of 50 Hz or less because integration in such an imager renders them indistinguishable from background.

Abstract: A vehicle arresting device comprises a net intended to be laid flat on the ground in the path of a target vehicle with an array of upwardly-directed spikes attached to the net along a leading portion, so that when a vehicle runs over the device some of the spikes engage in its front tires and the net is caused to wrap around the front wheels, being pulled tight under the vehicle to prevent further rotation of those wheels. There are two rows of spikes, with the spikes in the second row being substantially longer than the spikes in the leading row. The gauge of the netting also varies, with the leading strip which includes the shorter spikes and back towards the longer spikes being of a thinner gauge, the portion from the longer spikes back to approximately the mid length of the net being of a thicker gauge, and the trailing portion reverting to the thinner gauge. These measures help to ensure that the net is capable of arresting a wide range of vehicles, from passenger cars to trucks.

Abstract: Reader apparatus for receiving data from a transponder in the body of a patient, for example a femoral nail. The apparatus includes an antenna which can be varied in size and shape to fit patients, the size and shape of whose bodies vary significantly. A variable impedance unit is included to maximise power matching between the antenna and a reader unit for a given antenna configuration.

Abstract: An electric propulsion system including a plasma chamber having a first output aperture having first acceleration and screen grids, and a second output aperture having second acceleration and screen grids. The screen grids are maintained at a constant positive potential. In use, ions are expelled from the two apertures in anti-parallel directions. By independently controlling the potentials of the acceleration grids to adjust the rates of ion extraction from the output apertures, small resultant thrusts at the ?N level may be obtained and the resultant thrust maybe continuously reduced to zero. By closing off apertures of one of the screen grids, thrust at the mN may be obtained with sub-?N accuracy. The system therefore provides functionality previously achievable only with plural types of electric propulsion system, providing weight and complexity savings for satellites or space-probes comprising such systems.

Abstract: An electrode assembly is formed by respectively overlaying a sheet cathode 1, a sheet separator 3 and a double-sided sheet anode 8 to form a stacked structure 10, and subjecting the stacked structure to multiple folds, wherein the initial fold comprises folding the cathode in half around the double-sided anode so as to surround the respective upper and lower active anode surfaces thereof. The multiple folds may comprise one or more subsequent parallel folds made with the fold line D-D extending perpendicular to the original length of the stacked structure such that its overall length is halved at each fold. A pouch battery comprising said electrode assembly has improved safety and performance characteristics. The pouch battery construction has especial application to lithium primary batteries.

Abstract: A method of anomaly detection applicable to telecommunications or retail fraud or software vulnerabilities uses inductive logic programming to develop anomaly characterization rules from relevant background knowledge and a training data set, which includes positive anomaly samples of data covered by rules. Data samples include 1 or 0 indicating association or otherwise with anomalies. An anomaly is detected by a rule having condition set which the anomaly fu,lfils. Rules are developed by addition of conditions and unification of variables, and are filtered to remove duplicates, equivalents, symmetric rules and unnecessary conditions. Overfitting of noisy data is avoided by an encoding cost criterion. Termination of rule construction involves criteria of rule length, absence of negative examples, rule significance and accuracy, and absence of recent refinement.

Abstract: A molecular single electron transistor (MSET) detector device (14) is described that comprises at least one organic molecule (87) connecting a drain electrode (84) and a source electrode (82). In use, said at least one organic molecule (87) provides a quantum confinement region. At least one analyte receptor site (90, 92) is provided in the vicinity of said at least one organic molecule (87) that bind molecules of interest (analytes). A fluid analyser (2) is also described that includes the MSET detector, a pre-concentrator (4) and a fluid gating structure (6). The fluid gating structure (6) is arranged to selectively route fluid from the pre-concentrator (4) to either one of the detector (14) and an exhaust port (12). The pre-concentrator (4), fluid gating structure (6) and detector (14) are each formed as substantially planar layers and arranged in a stack or cube.

Abstract: A method of processing for a coded aperture imaging apparatus which is useful for target identification and tracking. The method uses a statistical scene model and, preferably using several frames of data, determines a likelihood of the position and/or velocity of one or more targets assumed to be in the scene. The method preferably applies a recursive Bayesian filter or Bayesian batch filter to determine a probability distribution of likely state parameters. The method acts upon the acquired data directly without requiring any processing to form an image.

Abstract: A barrier adapted to be set up for temporary traffic control comprises a man-portable unit placed on the ground from which a boom, preferably in the form of a reelable tube, can be withdrawn. The boom extends at an oblique angle to the ground in its “down” position and a motor within the ground-standing unit can raise and lower it between that position and an “up” position at a greater angle to the ground in which traffic can pass.

Abstract: Method and apparatus for mitigating the effects of security threat involving malicious code concealed in computer files (for example computer viruses, etc.). The method operates by inserting additional strings of arbitrary length within computer files of known type which may contain such security threats. The strings are chosen to have no substantial effect on the files in normal operation, but potentially disrupt attack code located in the file. Inserted sequences may incorporate a character sequence which, if interpreted as code, halts execution of that program. Alternatively, or in addition, character sequences may be deleted or reordered provided that they have no effect on normal interpretation of the file. As a result, the effect of malicious code operating successfully as intended by an attacker may be mitigated. The methods do not require prior knowledge of the nature of a specific threat and so provide threat mitigation for previously unidentified threats.

Abstract: A method of histological assessment of nuclear pleomorphism to identify potential cell nuclei divides image data into overlapping sub-images. It uses principal component analysis to derive monochromatic image data, followed by Otsu thresholding to produce a binary image. It removes image regions at sub-image boundaries, unsuitably small image regions and holes in relatively large image regions. It then reassembles the resulting sub-images into a single image. Perimeters (P) and areas (A) of image regions which are potential cell nuclei are determined and used in calculating nuclear shape factors P2/A. Nuclear pleomorphism is assessed as relatively low, moderate or high according to whether predetermined shape factor thresholds indicate a mean cell nucleus shape factor for an image is relatively low, moderate or high.

Abstract: Direction findings by radio comprises arraigning an array of antennas, to receive signals from emitters, selecting individual antenna signals using a first multipole switch and determining, antenna signal strengths. Individual antenna signals are also selected by mutipole switch, which routes a selected signal to a third multipole switch. The third switch switches a phase shifter into and out of an antenna signal path. An adder is employed to add an antenna signal in a first signal path extending via the first multipole switch to a different antenna signal in a second signal path extending via the second and third switches. This determines combined signal strengths between pairs of antenna signals, one of which either has or has not been relatively phase shifted depending on the third switch position. Covariance matrix elements are determined from signal strengths enabling emitter bearings to be derived.

Abstract: A self-energising brake assembly, particularly for braking a drive shaft of a heavy tracked vehicle such as a tank, has a pair of discs carrying friction pads borne to rotate with the shaft. These friction discs are located to either side of a central non-rotating water-cooled disc assembly. A control brake disc is also borne to rotate with the shaft but capable of turning relative to the same via a ball screw assembly. To apply the brake the control disc is retarded relative to the shaft by means of an associated caliper, which causes relative axial movement between the inner and outer rings of the ball screw. This movement drives the friction disc axially along the shaft, on a ball spline, towards the friction disc, thus clamping the non-rotating disc between the two friction discs and braking the shaft.

Abstract: An electrically steerable phased array antenna system includes an array of antenna elements and a corporate feed network having an inner region for input of two input signals A and B. The corporate feed network has two outer regions and generating vector combinations of respective input signals and other input signal fractions. Each outer region has a splitting and combining network providing the vector combinations as signals to antenna elements connected predominantly peripherally to itself. Each splitting and combining network has input signal connections from the inner region disposed peripherally of the corporate feed network. Each consists of splitters and adding/subtracting elements implemented as hybrid couplers some of which have re-entrant or meandered track sections. Hybrid meandered track sections have multiple widths for signal weighting. The corporate feed network is configured to avoid track cross-overs.

Abstract: A system for stabilizing video signals generated by a video camera which may be mounted in an unstable manner includes a digital processing means for manipulation of each incoming image that attempts to overlay features of the current image onto similar features of a previous image. A mask is used that prevents parts of the image that are likely to cause errors in the overlaying process from being used in the calculation of the required movement to be applied to the image. The mask may include areas where small movements of the image have been detected, and many also include areas where image anomalies including excess noise have been detected. The invention also discloses means for dealing with wanted movements of the camera, such as pan or zoom, and also discloses means for dealing with the edges of video signals as processed by the system. A method is also disclosed.

Abstract: A sheet of thermally reflective material (1) has a surface texture comprising a plurality of reflecting elements (2), wherein each element has a first facet (4) which is substantially reflective at thermal infrared wavelengths and wherein the respective first facets (4) form an angle ? with the plane of the sheet (A-B) (0°<?<90°). Preferably, the first facets (4) are aligned such that, in use, thermal radiation is reflected from a common direction. By orienting the sheet of thermally reflective material to reflect cold regions of the sky, a marking material exhibiting a cold spot in a thermal imager can be provided.

Abstract: A sabot 7 having a rearward end and a central longitudinal channel 1 which is engageable with projectile 33 has an anisotropic compressive strength distribution such that on individual radial planes the compressive strength in a first principal material direction P1 radiates from the central channel 1 towards the rearward end of the sabot. This permits a more even distribution of force at the interface between the sabot and the penetrator. The sabot may be constructed from a fibre reinforced plastic composite, containing a single or a double array of fibres.