Abstract: An amplifier arrangement suitable for use in a receiver for use in a telecommunications system is described. The arrangement includes an amplifier and an FET switch arrangement arranged to alter the time constant of the amplifier in dependence upon the incident signal frequency. A balance switch arrangement is arranged such that switching transients of the switch arrangement are cancelled out in the amplifier arrangement.

Abstract: An optical resonant assembly which comprises a plurality of partially light-transmitting mirrors, a layer of photochromic material disposed between the mirrors, a light source providing a light beam of variable intensity incident on the layer of photochromic material and detecting means for determining transmittance values of said incident beam at different intensity levels, said photochromic material having a low quantum yield for bleaching with light of a wavelength corresponding to said light beam and being selected from pyran compounds of the general formula (I) below: ##STR1## wherein X and Y together represent a spiro-adamantylidene group or a spiro-carbocyclic or heterocyclic group or X and Y independently represent hydrogen, alkyl (preferably lower alkyl having 1 to 5 carbon atoms) or phenyl and R.sub.3 and R.sub.4 each independently represent hydrogen, alkyl, aralkyl, aryl, halogen or a heterocyclic group and R.sup.

Abstract: In a forty megabit per second TDM signalling system in which twenty 2 megabit per second signalling streams are combined, one of the twenty primary signalling streams is inverted by the circuit arrangement and substituted for one of the other signalling streams. By using adjacent channels the forty megabit signal stream has a guaranteed change of data at least once every twenty bits. The system facilitates clock recovery and synchronization in apparatus employing bi-phase mark encoded data.

Abstract: In order to permit multislot connections to be simply made across a telecommunications digital switch, so that all the slots of the multislot connection experience the same whole frame time delay, the switch is constructed as input and output switch stages each comprising arrays of digital switching modules (DSM) and a central switching area comprising two arrays of Demultiplexing/Mixing/Remultiplexing devices (DMR) interconnected by an array of digital switching modules (DSM), wherein each DMR has a transfer function such that a channel (p) in a time frame of (q) channels on an input line (r) appears on an output line (s) which is related to the input line by means of a backward rotate function, where s=MOD (q-r+p), where MOD=modulo q. This construction of switch ensures that all channels routed through the switch have one of only two possible values of whole frame time delay, thereby simplifying the setting up of a multislot connection.

Abstract: A wideband/multislot switching arrangement is provided for use in a digital telecommunications exchange. A call handling device is provided which receives signalling information about a path connection, and which communicates with a switch interface to generate a single switch request. The switch interface includes a map record of each circuit connection controlled by the call handling device and generates multiple switch requests which are used to control a number of switches to make the path connections.

Abstract: In order to reduce thermal coupling between diodes in a light emitting diode array for a printing or imaging system which has the undesirable effect of wavelength shift and output reductions, rows (12, 14) of diodes are provided which are separated and inclined to the direction (Y) of scanning movement during a print operation, wherein current pulses applied to the diodes of each row for energization are delayed with respect to one another such that energization and printing occurs in a line perpendicular to the direction of scanning movement.

Abstract: The synchronization arrangement includes a waveform and synchronization information generator to supply synchronization information for transmission with a data stream over digital switching networks. The synchronization information includes two different patterns, phased displaced with respect to each other. Interfaces connect peripheral devices to the networks and are adapted to detect a validate the synchronization information. The checks made are in respect of detecting both patterns, the amount of phase displacement, and the correct sequence. If the synchronization information is invalid, the detecting interface selects a data stream from another network exclusively for use by the corresponding peripheral device.

Abstract: The invention relates to a photochromic gamma butyrolactone having the general formula (I): ##STR1## in which X represents >CH.sub.2 or >C(CH.sub.3).sub.2 ; R.sub.1, R.sub.2 and R.sub.4 independently represent a group selected from hydrogen, alkyl or aryl (including substituted aryl), with the proviso that one of R.sub.1 and R.sub.2 is always hydrogen, and R.sub.3 is a 3-thienyl, 3-furyl, 3-benzothienyl or 3-benzofuryl group in which the 2-position is substituted with an alkyl, aralkyl or aryl group (including substituted aryl).The lactones are useful in photolithography and in the production of security inks and markings and in the production of data recording materials.

Abstract: A security arrangement for a telecommunications system having two security planes, a plurality of peripherals, a plurality of peripheral communication controllers; and switching arrangements interconnecting the peripheral communication controllers. To determine a faulty security plane, a duplex path is provided between the controllers, and, using this path, a controller automatically performs path checks on one of the security planes. If the plane is found to be not faulty, the controller sends data associated with that plane to the peripheral with which it is in communication.

Abstract: An optical waveguide and method of fabricating waveguide structures is disclosed. More specifically, a method of producing an organic waveguide which comprises treating a transparent plastic substrate with a solution in a inert solvent of an organic dopant which is absorbed into the surface of the substrate, under conditions such that a surface layer is formed having a refractive index which is greater than that of the substrate. Said dopant has a higher affinity for the plastic's substrate than for the solvent.

Abstract: A series of novel photochromic spiropyrans are disclosed in which a spiro-adamantane group is introduced into the 2-position of the benzopyran or naphthopyran ring. The spiropyran compounds of the invention exhibit heliochromic properties, i.e. they color in sunlight and fade rapidly at ambient temperatures in the absence of U.V. light, making them good candidates for use in the manufacture of sunglasses. The invention includes lenses which darken in sunlight and incorporate the novel spiropyrans and a process for the preparation of the spiropyran compounds.

Abstract: Photoreactive plastics lenses are disclosed which are coated or impregnated with an adamantane 2-spiro-benzo or naphthopyran and with a blue coloring photochromic benzo- or naphthopyran having a nitrogen containing substituent in the 2-position in the pyran ring. The lenses darken in sunlight and fade rapidly at ambient temperatures in the dark or in white light which does not contain a U.V. component. The combination of the yellow/orange coloring adamantane 2-spiro pyran compound with the purple/blue coloring pyran gives a desired brown/grey coloration in the sunlight-darkened lens. The invention includes novel blue-coloring pyran compounds in which the nitrogen-containing substituent in the 2-position is a phenyl group having an amino or substituted amino or nitrogen-containing heterocyclic substituent in the ortho- or para-position of the phenyl group.

Abstract: A photochromic ink composition which comprises a solution of a 1,2-dihydroquinoline (DHQ) in a polymer solution, the dihydroquinoline being sensitive or sensitized to ultra-violet light.

Abstract: The Telecommunications system includes at least two exchanges and a plurality of user equipments. Each equipment includes a store for holding a user variable data word particular to that user. Each exchange is provided with a store for holding all the user variable data words of the users connected to it, and each exchange is also provided with its own random variable data word. When a first user makes a secure call to a second user, the first user equipment encrypts the call using its particular variable data word and sends the encrypted data to its own exchange. The exchange decrypts the call using the particular user variable data word that will be used for the call. The exchange encrypts the random variable data word with the particular user variable data word and returns it to the first user. The exchange also sends the random variable data word to the second user's exchange which encrypts it with the user variable data word particular to the second user, and sends it to the second user.

Abstract: A series of novel 3-pyrryl fulgides and fulgimides are disclosed which are photochromic. The photochromic compounds are coloured by subjecting them to irradiation in the near ultraviolet and will revert to the colourless form on exposure to visible light, especially light having a wavelength in 600 to 650 nm band.

Abstract: A series of photochromic compounds are disclosed which have the property of undergoing a reversible color change when exposed to unfiltered sunlight and reverting to their original color in the absence of U.V. light at room temperature. These compounds have the general formula: ##STR1## represents an adamantylidene or a substituted adamantylidene group;R.sub.1 represents hydrogen, alkyl, aryl, aralkyl or a heterocyclic group,X represents oxygen or > NR.sub.2, in which R.sub.2 is hydrogen, aryl, alkyl or aralkyl and ##STR2## represents an aromatic group, an unsaturated heterocyclic group or a benzannelated heterocyclic group.The photochromic compounds of the invention are useful in the manufacture of photoreactive lenses, particularly plastic lenses.

Abstract: The arrangement is for controlling speech communication in a communications exchange. The speech transmission is handled by a switchblock composed of a number of digital switching modules interconnected by a plurality of wire connections, and requiring the speech signals to be accompanied by bit and frame clock references to allow a receiving module to align the incoming data to its clock reference. The wire connections which carry frame synchronization information also carry control data which is bit interleaved with the frame synchronization information. Circuit means is provided which receives the bit interleaved frame synchronization information and control data, and demultiplexes the frame synchronization and control data to provide a retimed control data signal for use at the receiving module.

Abstract: An aligner (FIG. 1), which has seven registers SRGA to SRGG each of 64 bits in length, is used to align incoming line signals to exchange data rate and to convert exchange rate data signals into line rate data signals. The aligner behaves as a variable delay and is required to operate in any one of three modes; (i) frame aligning 2,048 k Bits/second line signals to a 2,048 k Bits/second exchange rate, (ii) aligning 1,544 k Bits/second line signal to a 2,048 k Bits/second exchange rate and (iii) converting a 2,048 k Bits/second exchange rate to a 1,544 k Bits/second line rate. In the third mode of operation it is necessary to derive the line clock from the exchange local clock. This is achieved by forming a phase-locked loop (FIG. 5) incorporating the delay of a standard aligner and driving the loop with the exchange frame reset signal (f IN).

Abstract: The method of growth of the digital switchblock is for use in telecommunications. The switchblock comprises a plurality of superplanes each including a plurality of central digital switching modules interconnected to a plurality of demultiplexer-mixer-remultiplexer stages; and, a plurality of outer digital switching modules connected to the demultiplexer-mixer-remultiplexer stages on each side of the superplanes. The outer digital switching modules are increased linearly as the number of telecommunication lines is increased from a first order of telecommunication lines. The number of superplanes is increased linearly as the number of telecommunication lines increase from the first order of telecommunication lines to a second order of telecommunication lines and thereafter remain constant as the number of lines increase.

Abstract: A method is disclosed for manufacturing transparent plastic articles, primarily plano or opthalmic photoreactive lenses, which comprises incorporating fulgides or fulgimides containing an adamantylidene group in plastics casting or moulding compositions or preformed plastics articles and converting the fulgide or fulgimide in situ into a form in which it confers on the article the property of darkening in the presence of sunlight and fading in its absence.