摘要:

Nearly all the papers on cellular logic published recently have dealt with arithmetical functions. This paper proposes other areas where cellular logic may be usefully employed. These include switching arrays for computer highway control, arrays for signal routing in digital data networks and coding systems (e.g. where banks are online to a computer). Some examples of arrays for these applications are given.

DOI:10.1049/piee.1972.0166

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A model ionosphere, comprising electron-density and collision-frequency distributions for the midlatitude D region at summer noon during sunspot-maximum conditions, has been produced which will give satisfactory results for propagation at low and very low frequencies. The electron-density distribution above 68 km was based on a distribution, measured in a rocket, which was altered until fullwave calculations using it gave propagation parameters in agreement with the average observed values. Below 68 km, a C layer was found necessary to give the best fit to measured ground-interference patterns at 16 kHz. A comparison is also shown between a measured pattern of this kind and one calculated from the rocket distribution, which was obtained on the same day.

DOI:10.1049/piee.1972.0168

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The dispersion characteristics of electromagnetic fields are examined for waves propagating in a medium with a permittivity which is modulated periodically with respect to time and one spatial co-ordinate. By taking a guided-wave approach, which expresses the fields of arbitrary sources in terms of a superposition of modal solutions, it is shown that many properties of the individual modes may be inferred by means of wavenumber diagrams. These diagrams are easily constructed for the special case of a vanishingly small periodic modulation. By using coupled-mode consideration, this special case is extended to serve as a good approximation for finite modulation amplitudes. In addition to yielding information on the dispersion character of modal fields, it is shown that the wavenumber diagrams may be employed to extract the modal constituents of a plane wave scattered by a layer containing a space-time periodic medium. The principal far-field components of waves excited by a localised arbitrary source embedded in such a medium may also easily be obtained from the wavenumber diagrams. The guided-wave approach, together with its associated wavenumber diagrams, is thus shown to serve as a powerful tool in analysing and understanding a large class of phenomena, which includes the diffraction of light by sound and parametric effects in nonlinear media, as well as other aspects of wave interactions in material bodies.

DOI:10.1049/piee.1972.0169

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A new kind of laser-beam modulator is described. An interdigital electrode structure deposited on an electro-optic crystal is used to produce a spatially periodic electric field which diffracts the laser beam within the crystal. Baseband operation is possible, and optical-pulse risetimes of 1.5 ns have been observed. The required drive power is only 7.5 nJ per pulse at 25 V, but this could be improved by scaling. The measured extinction ratio is 25 dB and this varies by less than ±1dB for a 10 K temperature change. The form of the modulator lends itself to inclusion in thin-film optical circuits.

DOI:10.1049/piee.1972.0170

出版商:IEE    

年代:1972

数据来源: IET

摘要:

Upper and lower bounds for the even- and odd-mode capacitances for the shielded-pair line are obtained in closed form using variational techniques that are applicable to inner conductors of arbitrary size and spacing. Results of computed normalised capacitances are catalogued in graphical form, together with an estimate of the error.

DOI:10.1049/piee.1972.0171

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The propagation coefficient for the current flowing in a Beverage aerial driven by a generator is derived from the compensation theorem. Comparison is made with measurements and with other theoretical methods. It is concluded that the attenuation increases approximately as the square root of the frequency, reaching a limiting value at high frequencies. The velocity of propagation is less than the free-space velocity, but tends towards it at high frequencies. Expressions for the characteristic impedance of the aerial are also given.

DOI:10.1049/piee.1972.0172

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The classical Woodward method for synthetising linear-aperture distributions by pattern sampling is shown here to give a hybrid form of edge behaviour, in which the aperture distribution for the even part terminates in a pedestal (edge exponent α = 0), while that for the odd part approaches zero linearly (α = 1). Hence the Woodward sampling functions are not the proper functions to use for representing an arbitrary aperture-limited function of either the order α = 0 or α = 1. Instead, a new set of sampling functions is constructed, for each order α = 0 and 1 separately, that is capable of representing exactly an arbitrary pattern space factor of that particular order.

DOI:10.1049/piee.1972.0173

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The basic theory and principle of operation of a new method of phase comparison for use in distance protection schemes is outlined. It is shown that the angular limits of comparison between signal pairs are determined by the setting of time-delay circuits, and that the new device is extremely variable. Comparator circuitry based on transistor logic is described in detail, and the effect of setting errors is analysed. The output from the device progresses from a short-duration pulse at the threshold to one of fixed duration, and the implications of such a response with regard to the overall performance are established. An introduction to generalised multi-input comparators is given, which, unlike conventional multisignal techniques, can be adjusted to give dissimilar limits of comparison between each signal pair.

DOI:10.1049/piee.1972.0175

出版商:IEE    

年代:1972

数据来源: IET

摘要:

A control philosophy is developed for a central digital computer to work online and to control the operation of a multiterminal h.v. d.c. system. It is assumed that each terminal of this system is equipped with fast analogue controllers of the conventional type which can accept commands from the central computer. The behaviour of a representative d.c. system has been tested on a laboratory model controlled under fault conditions by a PDP8 computer. It is shown that a satisfactory system-fault performance can be achieved with the philosophy and programming methods adopted.

DOI:10.1049/piee.1972.0176

出版商:IEE    

年代:1972

数据来源: IET

摘要:

The paper describes an interactive computer method for designing electricity-supply networks, which provides the engineer with a choice of outline designs near the optimum. The interactive mode is used, not only to harness directly the calculating power of the computer, but also specifically to enable the computer to participate in the design process as a simulated designer.An initial design is suggested, and a sequence of designs is evolved by a series of amendments, the control action coming from either the computer or the engineer. A sample of the total number of constraints for each design is checked to obtain a statistical estimate of the security of the complete network. The information from each sample is processed to give a formalised representation of those features which indicate the strengths and weaknesses of a design, which can then be treated by a special algorithm to determine the appropriate modifications. The method is illustrated by an example involving 17 substations. Experience of the method indicates that solutions for networks of realistic size can be obtained in economical computing time.

DOI:10.1049/piee.1972.0177

出版商:IEE    

年代:1972

数据来源: IET