Abstract: An electrode arrangement for an electrical impedance tomography system comprises a plurality of electrodes in an array mounted in a support medium for supporting the electrodes adjacent a surface of a volume the electrical conductivity distribution of which is to be measured, for example the thorax or another body part, a pipeline, the ground, and so on. The electrodes are disposed in two groups, the arrangement being such that, in use, one group will be closer to the surface than the other group, In operation, applying a known current to them. For each stimulated pair, a resulting potential difference will be recorded at the pair of the remaining electrodes which, if stimulated, would produce an electric field with vectors of the electric field produced by the stimulated pair of electrodes.

Abstract: A grenade machine gun or other weapon which employs superelevation of the barrel comprises a barrel unit and an aiming system mounted upon a support. The aiming system is mounted to the weapon and the support by a coupling unit. The aiming system comprises an imaging and display unit for displaying an image of a scene including a target, angle encoders for providing a signal representing displacement of the imaging unit in elevation relative to the support, and a control unit, e.g. a computer, for selecting either of two states for the coupling unit. The first state entrains the imaging unit to move with the barrel. The second state secures the imaging unit to the support and allows the barrel to move relative to both, i.e. during superelevation of the barrel. The coupling unit may comprise a first part connected to the weapon for rotation in elevation with the barrel unit and a second part connected to the imaging unit.

Abstract: In a wavelength-division multiplexer/demultiplexer of the free-space kind, which uses a diffraction grating or other angularly-dispersive element, spatially-shaping the light beam(s) to modify the passband response in the dispersion plane results in a substantially flat spectral response. Spatial shaping may be obtained using lenses disposed adjacent ports through which pass a corresponding plurality of angularly-dispersed light beams having different centre frequencies/wavelengths. Each lens may be a cylindrical lens with its cylindrical axis normal to the dispersion plane so as to shape the light beam in only one direction, i.e. that of the dispersion plane. The lenses may each be a single lens, conveniently a microlens, each adjacent a port through which WDM light beams pass. Alternatively, a plurality of microlenses may be provided adjacent the plurality of ports and a single microlens adjacent the single WDM port.

Abstract: A high speed analog-to-digital converter, for converting an analog input signal (u(t)) with a maximum frequency (Fmax) to a digital output signal (x(n)) with an output sampling rate (Fs) at least double the maximum frequency (Fmax), comprises a plurality of analog narrowband filters (F0-FM−1) for filtering the analog input signal (u(t)) to produce a corresponding plurality of narrowband signals (X0-XM−1), which is supplied to a corresponding plurality of analog-to-digital converter units (AD0-ADM−1). The converter also comprises sampling and summing circuitry for sampling the outputs of the analog-to-digital converter units sequentially at the predetermined sampling rate (Fs) and summing the resulting sampled signals to produce the digital output signal (x(n)).

Abstract: A method and apparatus for processing an input signal for transmission and/or storage, uses an analysis filter bank (21;51) to decompose the signal into sub-band signals which are used to modulate a plurality of carriers. The carriers are combined into a single encoded signal for transmission/storage. The encoder/decoder is especially applicable to telecommunications systems and recording systems. The analysis filter bank may comprise a multiresolution filter, such as an octave band filter bank (40A/B/C/D . . . 43A/B/C/D) implementing Discrete Wavelet Transform. The modulation may comprise double-sideband, single sideband, quadrature amplitude modulation, and so on. Where the input signal is analog, the carriers may be modulated directly by the sub-band signals. Where the input signal is digital, however, the sub-band signals are interpolated, all to the same rate, and then used to modulate the carriers.

Abstract: The purely bound electromagnetic modes of propagation supported by symmetric waveguide structures comprised of a thin lossy metal film of finite width embedded in an infinite homogeneous dielectric have been characterized at optical wavelengths. The modes supported are divided into four families depending on the symmetry of their fields. In addition to the four fundamental modes that exist, numerous higher order ones are supported as well. A nomenclature suitable for identifying all modes is discussed. The dispersion of the modes with film thickness and width has been assessed and the effects of varying the background permittivity on the characteristics of the modes determined. The frequency dependency of one of the modes has been investigated. The higher order modes have a cut-off width, below which they are no longer propagated and some of the modes have a cut-off thickness.

Abstract: In order to avoid errors inherent in the measurement of electrical phase differences or pulse arrival time in relative group delay measurements, different optical signals have their intensity modulated at a common high frequency and different permutations are selected. The amplitudes of corresponding electrical signals are detected and phase differences are computed on the basis of trigonometrical relationships. Because the modulation frequency is known, time differences can be deduced. Apparatus for measuring the phase differences conveniently comprises a slotted wheel (26) which passes selected ones or both of the optical signals. One of the optical signals may be split to produce a third signal with a predetermined phase shift, e.g. about 90 degrees at the modulation frequency and the amplitudes of some possible permutations of the three optical signals used to compute the phase difference. The measurements may be used to compute chromatic dispersion, polarization mode dispersion, elongation, and so on.

Abstract: In a detection system for detecting intruders in the vicinity of a predetermined path or line defined by a distributed antenna, for example an open transmission line, an array of discrete antennas are provided alongside the distributed antenna and within a predetermined distance therefrom. The antennas are spaced apart from each other and the distributed antenna and define a plurality of detection zones. A radio frequency transmitter is connected to one of the distributed antenna and the array of discrete antennas, and a complementary receiver is connected to the other of the distributed antenna and the array of discrete antennas. A control unit controls the transmitter, receiver and array of antennas to exchange radio frequency energy several times via the distributed antenna and selected ones of the array of antennas and to detect perturbations caused by an intruder moving adjacent the path and adjacent a particular antenna.

Abstract: A mounting for mounting an article onto a support comprising upper and lower mounting members. Seating surfaces provided between the members retain the members in assembled relationship with the members immovably registered together in a first plane. Three spaced mounting member registration projections provide, in the assembly, contact between the mounting members in three spaced and staggered positions on opposite sides of one of the mounting members, and registration to hold the members immovably together in a second plane. Spring-loaded locking is provided to hold the members together when assembled. Preferably the registration projections are provided on one member upon guide surfaces which are converging and inclined towards a respective seating surface. Guide surfaces on the other member are correspondingly converging and inclined.

Abstract: An intrusion detection system comprises a plurality of sensors (2A . . . 2X) and a corresponding plurality of receivers (3A. . . 3X). Each receiver receives, via the associated sensor, radio frequency signals comprising a multiplicity of transmissions at different frequencies within a predetermined frequency spectrum. The receiver detects the radio frequency signals and computes, for each of a plurality of successive time intervals and for each of the transmission frequencies, a measurement of signal amplitude over the time interval; compares such signal amplitude measurement with at least one threshold and, if the amplitude exceeds the threshold for a predetermined time period, generates a potential alarm signal. A processor (4) compares potential alarm signals from a plurality of sensors and determines that an intrusion has occurred if the potential alarm signal for a particular station does not coincide with a potential alarm signal for a neighboring sensor.

Abstract: In an intrusion detection system of the kind which comprises a “leaky cable” or open transmission line and is used to determine the presence of objects, things or people moving in the vicinity of the leaky cable, a transmitting antenna and a receiving antenna, one of which is an open transmission line/leaky cable, are connected to a transmitter unit and a receiver unit, respectively. A control unit controls both the transmitter unit and the receiver unit, and causes the receiver unit to scan a preselected radio band, with the transmitter unit not transmitting, to detect one or more relatively quiet portions of the band in which instant received signal levels are lower than a predetermined threshold. The control unit selects a plurality of disparate frequencies in such one or more relatively quiet portions and subsequently causes the transmitter unit to transmit signals by way of the transmitting antenna at the disparate frequencies.

Abstract: Apparatus for measuring very low levels of polarization mode dispersion of optical devices, that is inexpensive, robust and portable, comprises a broadband source and a polarizer for directing substantially completely polarized broadband light into the device under test with the polarization in a plane substantially perpendicular to the propagation direction of the light. Light leaving the device is analyzed spectrally to produce a spectrum of intensity in dependence upon wavelength or frequency of such light for each of at least two mutually orthogonal polarization axes in a plane perpendicular to the propagation axis of the light leaving the device. The spectra are used to compute Stokes parameters s1, s2 and |s3| for each of a plurality of wavelengths within the bandwidth of the broadband light.

Abstract: An adjustable manhole cover frame suitable for mounting on a manhole basin has an outer ring, capable of resting on the top surface of the basin, and an inner ring engaging the outer ring by screw threads and having support for a manhole cover. The inner ring also has screw jacks having lower ends suitable for contacting the basin top and rotatable to lift the inner ring. The inner ring may be rotated within the outer ring to adjust the height of the manhole cover, and the screw jacks may be used both to stabilize the inner ring while the outer ring base remains close to or in contact with the top surface, and may also be used to lift both rings out of contact with the top surface when additional raising of the inner ring is required.

Abstract: An insulated gate field effect transistor dosimeter has a source and drain defining a channel region, a floating gate having a first portion extending over the channel region, and a second, larger portion extending away from said region, a control gate having at least a portion thereof overlapping a first part of the floating gate, and a charging gate overlapping a second part of the floating gate. The area of the second part of the floating gate is much smaller than the area of the first part, and the charging gate is separated from the channel region by the control gate. The dosimeter is charged, before irradiation, by connecting the source, drain and control gate to a common ground and applying a potential difference between the charging gate and the common ground. The charge is supplied to the floating gate by a path which does not require a significant electric stress to be created in the region of the gate oxide and the channel.

Abstract: A DCR telecommunications network comprises a plurality of network switching elements interconnected by circuit groups for carrying calls, and a network processor communicating with the network elements. If it cannot use a direct route to a neighbouring network element, the switching element may access a routing table containing alternate routes which are updated periodically by the network controller. The network functions as a group of nodes interconnected by links. Routing takes place on a node-to-node basis. At least one of the nodes is a virtual destination node, vis. a logical entity corresponding to a group of two or more components which are network elements. A link to the virtual destination node is a set of circuit groups connecting to its components. Final destinations outside the network can be associated with the virtual destination node as an intermediate destination node, thereby allowing a call to exit the DCR network via any of the components rather than via only one Unique Exit Gateway.

Abstract: A noise suppression circuit for a two-wire communications channel comprises a hybrid device, for example a hybrid transformer or circuit, for providing a differential mode signal corresponding to a differential signal received from the two-wire channel. A summing device extracts from the two-wires of the channel a common mode signal and supplies it to a noise estimation unit which derives from the common mode signal an estimate of a noise level in at least one frequency band having a bandwidth considerably narrower than an operating bandwidth for the channel. The noise estimation unit adjusts the amplitude of the noise estimate to correspond to the residual noise in the differential mode signal and subtracts it from the differential mode signal to produce a noise-suppressed output signal. A noise detection and control unit scans the operating band, identifies a frequency band having an instant highest noise level, and sets the noise estimation unit to the detected noisy band.

Abstract: A telephone network comprises at least one switching unit having a plurality of subscriber access lines each having an associated calling number and, a storage device storing a plurality of listings of destination numbers. Each listing is associated with a respective one of the calling numbers and defines defining a personalized local calling area for that particular calling number. The switching unit detects a destination number dialed by a caller setting up a call, accesses the personalized local calling area listing for that calling number, and compares the detected destination number with the selected listing to determine whether the call is local or long distance. Each of the listings may comprise numbers having between three and ten digits. Provision may be made for the subscriber to create the personalized calling area by adding entries to, or deleting entries from, a standard local calling area common to a group of subscribers.

Abstract: Apparatus for monitoring opening of sealed enclosures, especially, but not exclusively, sealed containers containing goods-in-transit, such as goods vehicles, maritime containers or transport containers of the kind carried by tractor-trailers, ships, trains or aeroplanes comprises a radio receiver unit having at least one antenna for reception of radio signals. The receiver unit is housed within the enclosure and operates to scan a predetermined band of radio frequencies, periodically or continuously, and detect a sudden change in signal level. When it detects such a change in radio signal level, the receiver generates an alarm signal. Alternatively, the receiver may detect the difference between internal and external radio signal levels and determine the container to have been opened if the difference is less than a preset threshold.

Abstract: A method of controlling call traffic in a telecommunication system by dynamically altering the rate at which offered calls are accepted includes the steps of successively determining the offered call rate, and accepting calls from the offered calls, at a lower rate, as the offered call rate increases. For accepting the offered calls, at least two call-gapping intervals are used. The method includes selecting the shorter gapping interval whenever the offered call rate is below a threshold value and the longer gapping interval whenever it is above that value.

Abstract: An "Intelligent" telecommunications network comprises a plurality of switching units interconnected by links and connected to a central computer unit by a data communication system. For dynamic routing of a call, a first switching unit responds to a destination address in a call to attempt a direct link to a neighboring switching unit and, in the event that the attempt is unsuccessful, issues to the central computer unit a message containing the destination address. The central computer unit uses the destination address to identify the unsuccessful link; (ii) updates a routing database to identify the link as unavailable; (iii) determines an alternative route for the call using a tandem node and (iv) compiles a return message including a network address for a tandem switching unit and transmits it to the first switching unit. The latter attempts to route the call via a link to the tandem unit which attempts to complete the call by a direct link to the destination switching unit.