Table of contents

Discusses the principles of electrochemical sensors designed for the in-vitro measurement of the partial pressures of gases of clinical interest in the blood. Theoretical models, electrochemical principles and geometrical design are considered in detail.

A new type of curved neutron monochromator is being developed, called a comb monochromator, due to its shape. The curvature is approximated by polygonisation. In consequence, the intrinsic crystal properties are not changed, the luminosity is decoupled from the focusing geometry. Several experiments with gamma rays and neutrons for testing a Cu comb show favourable results. By neutron measurements the authors found a peak reflectivity of 65% and short wings in the diffraction pattern. The FWHM is not affected seriously by bending. This type of monochromator is profitable in diffuse scattering investigations.

Reports on a Faraday magnetometer which permits reproducible magnetisation measurements at temperatures between 3 and 300K in magnetic fields up to 14 T. The force on a magnetic moment is generated by the natural field-gradient of a Bitter coil. The maximum of this field-gradient is about 1.2*10² T m^-1; the maximal product B_zdB_z/dz amounts to 1.2*10³ T² m^-1, compared to about 50 T² m^-1 for electromagnets with gradient pole shoes. The magnetometer measures magnetic moments with an accuracy of better than 5%, the sensitivity allows one to detect changes in magnetisation of at least 10^-8 A m² ( identical to 10^-5 emu).

A multi-channel, electro-optical turbidity meter has been developed with an operating range of 0-10000 parts per million by weight. The instrument is based on a pulsed-light system which eliminates ambient light effects. The turbidity meter is described in detail together with the specially developed calibration apparatus. The calibration characteristics of the system were found to agree well with previous theoretically derived expressions, thus easing the calibration requirements of the probe. Calibration results are presented for natural sands and polystyrene spheres both for finely graded samples and a sample having a broad spread of particle sizes. The instrument calibration was also found to be independent of mean particle velocity. The use of the instrument for measuring the concentration distribution in a transient sediment cloud is described and the results are shown to give a significant improvement in spatial and temporal resolution when compared with existing sampling methods.

A simple and inexpensive double beam photometer is described. The photometer can detect changes in optical absorption as small as one part in 10⁵. For ease of mechanical and optical construction, a DC system is used, and the unusual features of the design are aimed at reducing noise to a satisfactory level. These features include not using the electron multiplication stages of the photodetectors, and locking the light intensity via a feedback loop from the reference detector.

A simple and easily operated electronic circuit for direct measurement of the fill factor of solid cells is described. With the suggested device one can measure the fill factor of solar cells, if the short circuit current is in the range 1 mA-0.5 A and the open circuit voltage is below 1 V. The circuit can be modified to make possible the measurement of solar cells with too small or too great a value of current and voltage.

Describes the system configuration of a self-built microcomputerised mirror electron microscope which allows scanning of the sample voltage as well as automatic data acquisition and display. The use of a microprocessor system simplifies previously described measurement of the total electron reflection coefficient and of the work function variations, and allows future extensions.

An automatic demagnetisation system and automated measurement system of the unbalanced inductance bridge voltage is described. It enables measurements to be made of the reversible magnetic permeability decreasing with time after demagnetisation for the case of small relaxation strength with relaxation amplitude of the order of 0.1%.

A short-barrelled gas gun for impact studies with a length-to-diameter ratio of 69 has been designed and installed. The design considerations and parameters of gun performance are discussed. The measured projectile velocities (up to 550 m s^-1), are compared with the curves calculated by the dynamic gas theory.

Some different approaches to the problem of designing experiments which estimate the parameters of nonlinear models are discussed. The assumption in these approaches that the information in a set of data can be represented by a scalar is criticised, and the nonscalar discrimination information is proposed as the proper measure to use. The two-step decay example in Box and Lucas (1959) is used to illustrate the main points of the discussion.

A modified Langmuir film balance with a new type of pressure pick-up system is described. The pick-up system consists of a closed rectangular frame of Teflon-covered steel foil floating on the substrate surface. The deformation of the frame is measured by four strain gauges fixed to the frame in a symmetric arrangement. The gauges form a bridge circuit which is activated by a lock-in amplifier. The resolution of the film balance is better than 20 mu N m^-1. By switching the sensitivity settings of the lock-in amplifier, one can measure between 1-70 mN cm^-1 full scale range with the same device. The trough has been constructed of brass and massive Teflon parts. By avoiding the application of any adhesive the danger of impurity effects is minimised. The main advantage of the system is the extreme tightness. Thus both isotherms and isobars may be recorded at very low speed.

The paper describes a new multi-station apparatus for fatigue testing textile fibres by the technique of biaxial rotation over a pin. This involves the tension-compression of fibres which are rotated whilst bent around a pin. Ten fibres may be tested simultaneously in both gaseous and liquid environments and some initial results are presented. The tester features an inexpensive electronic control system based around a single board microcomputer and is readily adaptable to meet the changing and expanding needs of the user.

The performance of a time-to-amplitude converter was investigated for conversion rates as high as 10⁵ Hz. Both a degradation of the time resolution and a systematic change in calibration were observed. The effects could be important in measurements with excitation sources of short pulse duration and high repetition frequency such as synchrotrons or pulsed lasers, or in positron annihilation experiments.

The NMR probe described is simple and compact, using only a single common and inexpensive integrated circuit for the HF head. Its frequency is tunable over a single wide range by the use of a hyperabrupt tuning diode. Moreover, tuning by a varactor diode makes it possible to incorporate the probe into a device which is self-locking on the magnetic field and which tracks the field when it varies. The range chosen stretches from 1030*10^-4 T to 4130*10^-4 T.

An adiabatic calorimeter of the scanning ratio type is described, which combines easy operation with high precision. Scanning velocities from less than 1 mu K s^-1 up to 0.1K s^-1 can be achieved, and temperatures between 273K and 773K are accessible. The capability of the apparatus is demonstrated by measuring the heat capacity of a mixture of triethylamine and water of critical composition near the critical temperature.

The minimum zone, minimum circumscribing and maximum inscribing references (here grouped as 'bounding references') used in the measurement of roundness are investigated. Their behaviour is studied by formulating their definitions mathematically as optimisation problems. The advantages of limacon references, both for accuracy under practical measurement conditions and for computational convenience, are investigated and the relationships between these and circular references are discussed. The formulation leads to the development of efficient algorithms (which can be given simple geometric interpretations) for determining these references. The approach adopted is also believed to give a new insight into the interpretation of data derived from roundness measuring instruments with radius suppression.

Describes a new holographic method for obtaining, in a single exposure, the isochromatic lines and one isoclinic line of a photoelastic model in which a continuous wave (CW) laser operating in a TEM_infinity mode with internal mirrors was used.

A Pockels cell was investigated as an analogue shutter for laser-pulse shaping in materials processing and in material analysis. Many laser pulse shapes have been generated from the emission of a CW-YAG-laser or a pulsed free running YAG-laser, with this programmable Pockels cell. Typical rise time was 100 ns. Compensation of piezoelectric resonances of the Pockels cell crystal was possible.

Describes the design and performance of an optical instrument for neutrons with wavelengths around 2 nm containing a cylindrical neutron lens made of quartz glass. The apparatus will be used in a neutron beam deflection experiment aimed at reducing the upper limit of the electric charge of the neutron.

A new type of resistance thermometer for measurements of fluctuating and mean temperature in high gradient, two-dimensional thermal boundary layers is presented. With this thermometer the error originating from thermal interaction between wire and prongs caused by the temperature difference between the tip of the prongs and the gas can be easily eliminated. The thermometer is described in detail and measurements and error estimates in a temperature boundary layer are provided.

Compact helium-free atmospheric pressure HF/DF lasers were excited with a pre-ionisation-stabilised discharge scheme. The lasers produced megawatt outputs from H₂:SF₆ and D₂:SF₆ mixtures with plasma volumes of approximately 10³ mm³. The laser pulse durations were approximately 10 ns.

The optimum filter for improving the signal-to-noise ratio in a commonly encountered signal recovery situation is the ideal averaging filter. Approximants to the averaging filter response, with averaging times between 1 ms and 100 s, are realised by RC active networks having some novel properties. The use of these filters in place of the first-order low-pass filter leads to an improvement in the measurement rate by a factor of two or greater.

A scanning Fabry-Perot interferometer with 150 mm diameter plates has been built for use in spectral studies of faint atmospheric radiations. The instrument has been designed for usefulness over a wide region of the visible spectrum and at different spectral resolutions; the reflective plate coatings are a metal-dielectric combination, and plate separation can be varied easily over several centimetres. Scanning is achieved through piezoelectric plate spacing elements. Both plate parallelism and plate separation are servocontrolled, the latter with the aid of a highly linear and stable capacitive displacement transducer which directly measures changes in plate separation. Photoelectric detection and digital signal averaging and recording are used. The spectrometer has been applied to the study of winds and temperatures in the upper atmosphere through the measurement of Doppler line shift and broadening in airglow emission lines.

The authors constructed a thick-walled aluminium shield for biomagnetic measurements and measured its performance at 50 Hz in detail. These data show the difficulties in the construction of the door. The mechanical vibration is attenuated efficiently. The benefits of an aluminium shield in cost and construction over the mu -metal shield are discussed.

In the measurement of periodic fluid flows by laser anemometry, the velocities are often determined by sampling the Doppler signal at predetermined phase positions in the cycle. It is shown that the resulting intensity autocorrelation functions accumulated over many cycles are distorted by the sampling procedure. The form of this distortion is determined and verified experimentally. The application of a simple correction before the analysis of a correlogram is seen to greatly facilitate the measurement of mean velocities and turbulence level.

This work grew out of the need to know what instantaneous streamline patterns look like in unsteady inviscid two-dimensional flow as seen by different moving observers. A convenient fluid flow analogy was devised which makes use of the deflection properties of a membrane and moire fringes. The deflection properties also lead to an optical method for the measurement of pressure patterns at a rigid boundary in an experimental fluid flow situation. This method, when used in conjunction with closed circuit television and an on-line digital computer, enables one to obtain rapidly a graphic display of instantaneous and mean pressure patterns over an entire area of the boundary.

An electro-optical read-out system for measuring displacement and strain fields from a double exposure speckle photograph is described. The optical system uses a cylindrical element to project the 1-D Fourier transform cylindrical element to project the 1-D Fourier transform from a point on the photograph on to a self-scanning linear photodiode array, with minimal distortion of the spacing of the fringe pattern. The output from the array is processed electronically and fed to a computer which calculates displacements and strains. Experimental results obtained with a partially automated system show the accuracy and reliability achieved.

A circuit capable of producing bipolar square pulses of voltages up to +or-400 V, employing an integrated circuit timer and two mercury wetted relays is described. The frequency of the pulses can be varied from a cycle min^-1 to 2 kHz. A variable temperature sample chamber and the temperature control and measurement circuits are also described. The performance of the circuit is evaluated using samples of TGS and NaNO₂

The design and performance of a small hydrogen fluoride (HF) chemical laser excited by pulsed electric discharges between resistive (500 Omega mm) germanium electrodes is described. This laser has proved to be a highly reliable instrument during an extensive programme of optical investigations of semiconductors.

The instrument described is an improved version of a prototype described by Tanner (ibid., vol.12, p.957), and consists of a bellows, two fixed fluid resistors, a variable resistor, a sensor and a fluid flow detector.