Abstract: A terrain advisory system for an aircraft (A) comprises a processor (11) which compares terrain information, accessed from a memory (13) according to data from a navigation system (12), with dynamic flight parameters from a monitor (14) for the aircraft. The processor (11) also generates a trajectory signal and a pull-up signal to indicate, on a display (15), current aircraft trajectory relative to a line constructed from notional pull-up trajectories for the aircraft which avoid a predetermined clearance height without exceeding a predetermined acceleration acting on the aircraft during a pull-up maneuver.

Abstract: A latching mechanism for a sub-sea control module is constructed with energy storing means such that a latch is cooked into an unlatched condition by the action of lifting the sub-sea control module to store energy in the energy storing means and is moved into a latched condition by the action of lowering the sub-sea control module into abutment with the mounting base.

Abstract: An apparatus for cancelling vibrations includes a reference signal representative of the vibrations to be cancelled, an adaptive control filter producing an output signal based on the reference signal, and an actuator responsive to the output signal to produce vibrations which destructively interfere with the vibrations to be cancelled. The adaptive control filter comprises a circuit for transforming the reference signal into its frequency components, a processor for applying weights to these frequency components, and another circuit for combining the weighted frequency components to provide the output signal of the adaptive control filter. The circuit for transforming utilizes N integer updates of the reference signal to resolve the reference signal into its frequency components. Further, the circuit for transforming is updated n times between successive transformations of the reference signal into its frequency components, where 1<n<N.

Abstract: A specimen support for use in an electron microscope comprises a deposited diamond film. The film is deposited on a substrate using a plasma assisted chemical vapor deposition process and then machined to a desired configuration using a laser machining process. Molybdenum, tungsten or silicon are used as substrates.

Abstract: A modulating reflector circuit arrangement comprising a transistor configured by means of a feedback arrangement upon operation within a linear region of the transistor's current/voltage characteristic to reflect an incoming amplitude modulated signal with an increased amplitude and a modulator operable to modulate power to the transistor with a periodic waveform in which the reciprocal of the period of the periodic waveform is the required sideband frequency of the reflected signal and the waveform is selected such that the arrangement reflects a substantially single sideband signal.

Abstract: A method of proving the integrity of optical paths in an optical communication system wherein the same diagnostic optical signal is transmitted along each path from one end, and each path is provided at its other end with a grating pattern, for example, for producing a pattern of time spaced echoes of the diagnostic signal unique to that path. In one particular embodiment the diagnostic signal comprises an amplitude modulated optical signal and the echoes are produced at a time spacing such that the modulation components of the echoes are in-phase at a different frequency for each path.

Abstract: An acoustic sensor for use as part of a drill string in a borehole has an acoustic transducer which vibrates the drill bit in contact with the rock at the end of the borehole to generate acoustic signals in the rock. These acoustic signals propogate through the rocks ahead of the drill bit and are reflected and scattered to return to an acoustic sensor contained within the drill string.

Abstract: A continuous wave radar altimeter comprises a memory (24, 26), means for storing in the memory in digital form an array of return signals representative of the variation of reflected amplitude with path length, means (27), for addressing the memory for identifying a peak return representative of the highest objects on the terrain, means (28) responsive to the array for determining the signal-to-noise ratio thereof, and means (29) responsive to the height at which the said peak return occurs and to the signal-to-noise ratio to determine a "center of area" height representative of the lowest surface on the terrain. The altimeter thus provides not only the peak level, representing for example the tops of trees and buildings, but also the ground level.

Abstract: A continuous wave ranging system comprises a modulator for modulating an r.f. carrier signal in accordance with a pseudo random code, a transmitting antenna for radiating the signal towards a target, a receiving antenna and receiver for detecting the signal reflected from the target, a correlator for correlating the detected signal with the transmitted code with a selected phase shift corresponding to the current range gate to be tested, whereby the range of the target from the system may be determined, and filtering means for filtering from the output of the correlator those range gate amplitudes which vary with a frequency less than a predetermined value.

Abstract: The invention relates to a method of detection, a sensor and a test-kit which find application in immunological detection (e.g., immunoassay). The invention provides, inter alia, a method of detection, suitable for use in immunological detection of an entity, which method includes the use of a secondary species (as defined in the specification), the use of a first detectable species, and the use of a second detectable species. The method may include, for example, the use of a primary species, a secondary species, a first detectable species and a second detectable species. The primary species may be, for example, an antibody or a ligand. The secondary species may be, for example, an auxiliary species such as an auxiliary binder or an auxiliary ligand, or a species which has a part which is an auxiliary function. The entity to be detected may be an analyte species as such or may be an entity which carries or includes analytes species.

Abstract: An analog-to-digital converter includes an input for analog signals, a quantizer for producing a digital signal output, a feedback loop for feeding a signal derived from the digital output to be combined in analog form with the analog input for input to a filter. The output of the filter is fed to the quantizer. The filter comprises at least three filter stages. The filtered signal is derived using the output of at least one stage, other than the first stage, which is representative only of the response of the corresponding filter order and not of other filter orders. The output of the third stage is representative only of the third order response. A limiter is provided in the output of the third stage of the filter.

Abstract: A narrow and deep aperture is chemically etched in or through a body of, for example, cadmium mercury telluride or other infrared sensitive material. The etchant is constrained and etches faster adjacent to side walls of a mask on the body. Those side walls are sufficiently close to each other than the faster etching areas overlap. Apertures or slots having a width of about 7 um may be etched in this manner through a thickness of about 5 um via windows having a width of about 3 um in a photo resist of a thickness between 4 and 5 um.

Abstract: A switching arrangement for establishing a signal path between any one of a plurality of first ports and a common port and for varying the attenuation of at least one of the ports comprises in the signal path of each attenuatable port a first switching element and attenuating circuitry connectable by further switching circuitry across the first switching element, the first switching element constituting the sole series element in that path. The attenuating circuitry comprises a resistive network and the further switching circuitry comprises second switching elements connected to respective ends of the first switching element and to respective points of the resistive network for introducing one of a number of resistive states into the signal path.

Abstract: A helmet display system is provided comprising a display visor 3 located on helmet 1 on which helmet is also positioned image projection means for projecting an image via a holographic combiner 4 on the display visor 3. The helmet further comprises an anti-glare visor 2 which has optical transmission characteristics similar to those of a neutral density visor, with the exception that these characteristics are modified to compensate for the low transmission value of the display visor 3 to frequencies within a narrow waveband to which the combiner 4 is tuned. The invention provides a helmet display system which can be used in conjunction with an aircraft head-up display if required.

Abstract: In a magnetic resonance apparatus including a transducer (25, 31 ) positioned in the examination region of the apparatus, the transducer is connected with equipment (49) outside the examination region by way of a lead (47) which is grounded (51, 53) to signals of the frequency of the RF field applied to a subject (5) in the examination region to excite magnetic resonance in the subject, at a distance along the lead from the transducer equal to a quarter wavelength at the RF field frequency (or an odd multiple thereof). Distortion of the RF field due to loading by the transducer is thereby reduced. The transducer may, for example, be a microphone or loudspeaker, e.g. incorporated in an intercom or active noise reduction arrangement, or a sensor for sensing a condition of a patient being examined.

Abstract: In a exhaust smoke sensor a light emitter generates a light beam which passes through a region containing the exhaust gas to a first light sensor. To reduce interference the light emitter is driven by a near square wave signal produced by passing a square wave through a low pass filter.

Abstract: In a conventional sigma-delta converter/modulator, quantisation noise of the quantiser which produces the digital output is suppressed because of a feedback loop which feeds an error signal via a filter to the quantiser, the error signal being the difference between the digital output and the input. Improved noise suppression is achieved by more filter stages, but such converter/modulators require special measures to reset them in the event of an overload i.e. a high input signal. A modified output is taken from the filter which is such that a second filter appears, when the main loop is not overloaded, to be in a loop with a simple delay, i.e. a sigma-delta circuit. The main loop has the inherent recovery properties of a second order modulator/converter and cannot be swamped by the signal from the second loop because of a limiter and, when the main loop has recovered, so does the second loop containing second filter. However, the quantisation noise is now suppressed by the combined filters.

Abstract: In a magnetic resonance apparatus including an active noise reduction arrangement (9, 49, 51, 53) for use by a patient (5) undergoing examination in the apparatus the transducers (25, 31) of the arrangement are non-magnetic, e.g. are of the electret, piezoelectric or condenser type, and have no parts of ferromagnetic material.

Abstract: A helmet mounted display system comprising: a transparent visor; and an optical system which directs rays of light from a display produced by a display source onto a spherical region of the visor to provide by reflection at the visor, at a helmet wearer's eye position, a collimated virtual image of the display on a line of sight of a wearer of the helmet through the visor; the region of the visor being of a shape which is rotationally symmetric about a first axis and the optical system being mounted for rotation about the first axis, thereby to allow rotation of the eye position about the axis.

Abstract: A ferro-electric liquid crystal device comprises a substrate having a surface alignment layer, the surface alignment layer providing a pre-tilt angle .beta..gtoreq.10.degree. with directors of a nematic liquid crystal. Smectic liquid crystal layers of the device have a C2 chevron configuration with a chevron angle .delta. in the range of 2.degree..ltoreq..delta..ltoreq.15.degree., the C2 chevron being such that .theta..sub.c -.delta..gtoreq..beta., wherein .beta. is the pre-tilt angle, .theta..sub.c is one half of chiral smectic cone angle and .delta. is a chevron angle. A bistable switching angle .theta.s of the device is .gtoreq.12.degree.. A method of producing such ferro-electric liquid crystal devices comprises the steps of providing a liquid crystal device having the surface alignment layer and C1 chevron structure only and applying a low frequency (.ltoreq.500 Hz) and low voltage (.ltoreq.