Table of contents

A random access fixed store is described, which has a capacity of more than 3 million bits and an access time of the order of 5 μs. The storage medium is a photographic emulsion, accessed by a high resolution cathode-ray tube as light source and 10 stage photomultipliers as detectors. Addressing is under the control of an optoelectronic, closed loop cathode-ray tube beam positioning system, and parallel readout of 50 bits is achieved by optical multiplexing, by means of a square cross section mirror tunnel.

Recent developments in train control systems are aimed towards communication, by non-visual means, of information required for safety. In the British Railways system, all fixed data are generated by a binary coded telegram produced from phase discrimination of signals from trackside coils, energized with a high frequency carrier.

An electromechanical high speed uncapping shutter has been developed, capable of uncapping a 2·7 in diameter aperture in periods of 200, 180 or 125 μs. The opening action is obtained by discharging a capacitor between two metal conductor-foil arrangements; the foils are compressed and collapsed by the electromagnetic forces generated both in the foil elements and the adjacent conductor during the surge discharge. Some of the factors affecting the design, development and operation of the circuit are considered, including the energy input to the foil. Observations on the mechanism of collapse are discussed.

A trace detector for continuous and on-line monitoring of contaminants such as oil in water is described. The principle used is detection of the visible fluorescence emitted when the process fluid is irradiated with ultraviolet energy. Concentrations as low as 0·1 × 10⁻⁶ can be detected, but the instrument also overcomes problems associated with measurement of very high concentrations.

Capacitive displacement transducers can be a particularly accurate and sensitive means of measuring displacement over a wide range. They are equivalent to an almost perfect potential divider and when used with inductive ratio arms accuracies to 1 in 10⁶ can be achieved. Resolution of better than 1 in 10⁷ is possible and apart from environmental and structural stability a displacement of less than 40 Å can be observed.

A practical means of examining a sequence of frames from a ciné film by superimposing projected images is described.

Recent experiments on the interaction of proton beams with solids have shown that the regular variations of intensity in the spatial distribution of the scattered beam was dependent on the regular nature of the crystalline lattice. This phenomenon has been exploited in an apparatus which may be applied to the orientation and examination of single crystals and thin crystalline films. In the proton scattering microscope to be described, a beam of protons is directed on to the crystal under investigation and the scattered beam is observed directly on a fluorescent screen.

Holographic multiplexing has been used to produce three-dimensional reconstructions of people and outdoor scenes. Three-dimensional X-ray pictures have also been produced. These and other uses for multiple holograms are described. Single exposure holograms have been made of objects moving non-periodically and interference fringes have been observed in the reconstructions.

A description is given of two instruments developed to provide, in combination, absolute on-stream measurement of the mass flow of powdered materials. The range of application is typically to duct diameters from 0·1 to 0·6 m, with powders of top size not exceeding 500 μm and mass flows from about 1 to 20 kg s⁻¹. The instruments described are an ultrasonic velocity meter and a density meter relying on β-ray attenuation. The velocity meter measures the carrier air velocity, but it has been shown theoretically that for a wide range of conditions the mean slip between air and particles is small and calculable, so that measurement of the air velocity yields the solid velocity. The β-ray absorption gauge achieves a mean value of the density across a diameter by incorporation of a collimation system that obviates errors that would otherwise arise owing to non-uniform flow distribution across the pipe. The combined instrument is capable of measuring mass flow to 5% or better and has the advantage of not requiring the insertion of impedances into the flow.

An analogue counting unit is described which generates a continuously up-dated histogram display from a succession of measurements of a variable quantity. The unit is controlled by a classifier which allocates each measurement of an input signal to one of eleven classes, according to its deviation from a selected value, and shows the total number of measurements falling in each class on digital counters. The equipment is intended primarily for monitoring continuous production processes, although the classifier can also be used for the analysis of a particular set of measurements.

A recognition device for patterns presented in the form of a photographic transparency is described. The autocorrelation of the pattern is produced and identified by light levels on photovoltaic cells.

A napkin-ring torsion apparatus for the study of the shear properties of adhesive bonded joints is described. A high sensitivity capacitance-type extensometer is used for measuring the load-deformation characteristics of the adhesives. Angle of twist sensitivities as high as 6 × 10⁻⁸ radians can reliably be achieved. Shear stress is determined by using an extensometer to measure the strain developed in the metal adherends. The technique has been used with a variety of adhesive materials, having several glue-line thicknesses. Experimental variables include test temperature, strain rate, time at load and time between load-unload cycles.

A viscometer has been designed in which the sample under test is withdrawn through the capillary viscometer by means of a remote motor driven syringe pump, and the pressure developed across a finite length of the capillary is sensed through small holes bored through the wall and measured by means of a remotely placed differential pressure transducer. Liquid filled tubes connect the probe to both the pump and the transducer. The ratio of the pressure difference to the flow rate is proportional to the `apparent' viscosity of the sample. Tests on the laboratory bench with standard solutions indicate that a measurement with a standard deviation of about 0·7% can be attained on sample volumes of under 1 ml.

An approximate calibration of selected platinum resistance thermometers over the range from 2-273·15°K can be obtained by using only calibrations at the boiling point of helium and the ice point and at temperatures between 2°K and 4·2°K as given by helium vapour pressure thermometer measurements. Interpolation between these points is achieved by employing a table of Z functions for the range 4·2-273·15°K, and a polynomial equation in T against R for the range 2-16°K.

A review of the sources of error in continuous weighing at high temperatures shows that the following precautions must be taken in the design of accurate thermobalances: (i) insulation of microbalance from furnace heat; (ii) accurate control of the reaction temperature; (iii) effective earthing of glass components to avoid electrostatic charging; (iv) correction of weight readings for buoyancy forces; (v) use of a narrow reaction tube to minimize turbulence.

A new thermobalance has been designed with these precautions in mind. It also incorporates a novel divided gas flow system whereby the aerodynamic drag on the specimen from flowing gas is exactly balanced by a controlled opposite moment arising from a secondary gas flow. The thermobalance incorporates a Sartorius 4102 microbalance and weighs 1·5 g specimens to ±2 μg at 1273°K in flowing gas (e.g. O₂ at 0·25 ml s⁻¹ and atmospheric pressure).

An ENDOR spectrometer has been developed which is especially suitable for studying ligand hyperfine interactions. The complicated ligand ENDOR spectra are considerably simplified by alignment of the crystalline axes relative to the magnetic field direction. The process of alignment is facilitated by the provision of a reliable, precision-made crystal rotator in the microwave cavity, and by the observation of ENDOR lines on an oscilloscope. The crystal is situated within a small coil which efficiently provides an r.f. field at the sample, and the cavity geometry allows rotation in excess of ½π about an axis orthogonal to the rotation axis of the magnet. Amplitude modulation of the r.f. power has been found particularly suitable for chart presentation of ligand ENDOR spectra.

The results of a detailed calibration of a Jem 7, high resolution, electron microscope operating at 100 kv are reported in this paper. Three types of measurements have been made: (i) magnification as a function of intermediate and objective lens currents; (ii) camera constant and its dependence on objective lens current; (iii) relative rotations between the object, image and diffraction pattern. These data are sufficiently complete to satisfy the requirements of detailed, analytical, diffraction contrast experiments.

A simple, reliable device for continuously varying the intensity and plane of polarization of laser beams over a wide range is described. It consists of a series of transparent dielectric plates set at the Brewster angle and capable of rotation about the incident beam axis. This device has been used to control the beam intensities of a continuous wave helium-neon laser at a few microwatts and of a giant pulse Q-switched ruby laser at 200 MW.

An experimental study has been made of the imaging properties of a three-aperture electron-optical lens system. In general this lens has all three aperture potentials different from each other. An apparatus was constructed to determine the potential of the middle aperture required to maintain a constant image position while the potential of the last aperture (and hence of the image) is varied, the object position and potential being kept constant.

Modifications and readily assembled accessories are described for converting the manually operated photoelectric Fisher Autocytometer blood cell counter into a versatile automatic sampling and recording monitor for following growth curves in axenic unicell populations. Three versions of this equipment have been developed, between them covering a wide range of cell densities extending from a few dozen to 500 000 cells per ml. A batch sampling system is used for handling very low cell densities, continuous sampling with autodilution is used for high cell densities, and a recently developed model, in which the sample is pumped continuously through a sterile counting loop and returned to the parent culture, is suitable for use with very small culture cuvettes.

A small electrolytic humidity sensor of high sensitivity and speed of response is described.

A venetian blind particle multiplier has been examined to test its suitability for use in the measurement of ion-molecule specific reaction rates. Considerable variations in some of the characteristics of the multiplier have been observed over a period of several months. Nevertheless in a series of ion-molecule reactions of the type XH⁺ + XH -> XH₂⁺ + X the specific reaction rate measured by means of the multiplier agreed well with the same rates measured with a Faraday cup detector. Thus chemical discrimination effects which have been observed with electrostatically focused multipliers were not observed with this instrument.

With the development of fast film readers, photographic collection of x-ray data has become very attractive. Further improvement has been achieved by construction of a single crystal goniometer allowing collection of a large number of reflections on one film pack by using the oscillation technique. Overlap is greatly reduced with a special film cassette stepping device.

The construction, operation and uses are described of a resistance heated glass trap capable of maintaining temperatures ranging from - 196 to 0°C with only a small temperature gradient.

The construction of an inexpensive Dewar vessel which allows absorption and emission spectroscopy in the ultra-violet and visible, at controlled temperatures down to 77°K, is described.

Values of the energies of the E, G, H and I_a rays of Th B were obtained by use of a semicircular focusing magnetic spectrometer.

This note describes a simple hot wire probe found suitable for a wide range of anemometer applications.

A closed-circuit television system is described for routine calibration work on precision electrical indicating meters. Compared with an optical projector for reading meters, the television system is superior in screen luminance, depth of focus, length of scale shown with negligible parallax, and convenience of use.

In this note a camera is discussed for X-ray structural analysis of polycrystals, where the sharp focus of a tube, the sample and the reflection are placed upon the focusing circle.

Equations are derived which relate the instrumental linewidth in a back-reflection focusing camera (used in the study of polycrystalline materials) to the displacement of the x-ray source from the focusing circle along a diameter passing through the specimen centre; the two-dimensional problem is solved by assuming that the source is negligibly small but that the sample is finite.

In determinations of radiative lifetimes in which time intervals are measured up to the first detected photon, an error is introduced when subsequent photons are neglected. An accurate correction for this effect is described, having the advantages of general applicability and allowing the use of high photon detection rates. It is also shown that the error introduced by the use of this correction is negligible under all practical experimental conditions.

A simple reflectance fluorimeter has been developed for the determination of trace amounts of uranium by the sodium fluoride fusion method. The unit incorporates the electronic system of the Techtron AA3 atomic-absorption spectrophotometer. A method for the preparation of the fusion beads is also described.

In addition to reluctance of corner joints and stresses in the material, volt-ampere measurements at high flux densities are shown to be very dependent on the accuracy of the flux density measurement. As a result the air flux correction becomes important and methods of calculating or allowing for this factor are discussed in detail.

A simple, accurate gauge for the measurement of metallic projectile velocities is described. The method used is based on a time difference measurement (from an oscilloscope record) between two transient voltage pulses produced by a variation in inductance as a metallic projectile passes through each of two successive energized coils spaced a known distance apart.

A holder for kovar parts used for glass-to-metal sealing is described, which makes use of the widely different coefficients of expansion of steel and brass to prevent the kovar part from becoming loose in the holder when the holder and the kovar part are heated up to quite high temperatures during glass sealing.

This device, which avoids certain disadvantages of piezoelectric and magnetostriction transducers, gives a relatively large linear response and is controlled by a transistor circuit using relatively little power. A push-pull arrangement cancels ambient temperature effects.

A capacitance-type displacement meter has been developed. The instrument is very compact and light-weight, inexpensive to produce and easy to construct. The sensitivity of the instrument is satisfactory for most purposes served by these meters. The accuracy and stability of the instrument compare favourably with those of commerical meters.

A commerical colorimeter is modified for higher versatility and sensitivity. Applications to trace analyses for sulphur and lead are shown.